USE OF FENTANYL TRANSDERMAL SOLUTION OR METHADONE FOR PAIN CONTROL IN DOGS WITH ACUTE PANCREATITIS: PRELIMINARY STUDY

Introduction Pain management in patients with pancreatitis still appears problematic and complex. Recently a long-acting (96 hours) fentanyl transdermal solution (Recuvyra®) has been licensed for postoperative pain management in dogs. The aim of this study was to evaluate the analgesic efficacy of Recuvyra® in comparison with methadone during acute pancreatitis in dogs. Methods Twelve dogs with acute pancreatitis were enrolled in the study. Owners signed a consensus to enroll animal in the study. Dogs were randomly divided in two groups: one group received methadone (GM) (0.3 mg/kg, IV) and one group received fentanyl transdermal solution (GFT) at 2.6 mg/kg dosage. Both groups also received lidocaine 1 mg/kg IV followed by an infusion of 1-2 mg/kg/h for at least 48 hours. Because of the long onset of action (4 hours) the GFT received methadone (0.3 mg/kg IV) simultaneously with the transdermal solution application. Heart rate, respiratory rate, mean arterial pressure and temperature were recorded before the analgesic administration and after 4, 6, 8, 10, 12, 24, 32, 48 and 72 hours. Pain evaluation was done every 2 hours for the first twelve hours and every 4 hours until 72 hours, with a 4aVet pain scale. The operator in charge of pain assessment was unaware of the treatment done. When a score higher than 5 was recorded animals were treated with methadone IV 0.3 mg/kg (in GM) or 0.1 mg/kg (GFT) until a maximum dose of 0.6 mg/kg every 3 hours; the clinicians responsible for the drug administration were not the same assigned to the pain score evaluation. Results Two dogs (one for each group) were euthanized after 38 and 43 hours because of worsening of general conditions. All the surviving patients started eating after 32-48 from the beginning of therapy. Heart rate, in GFT, significantly decreased at T8 until T72 in comparison with T0. In GM pain score was significantly lower a T48 and T72 in comparison to T0, while in GFT scores recorded at T32, T48 and T72 were significantly lower in comparison to T0 (see table). No differences were recorded between the 2 groups. One dog of GFT received one dose of methadone 0.1 mg/kg IV. Mean dosage of methadone in GM was 0.53 ± 0.13 mg/kg every 3 hours. Discussion - Conclusion Recuvyra® was clinically effective in the control of pain during acute pancreatitis in dogs. Pain score decreased in both groups but in the GFT pain score was halved after 6 hours of treatment and only one dog needed rescue analgesia. The low number of cases could be the reason why significant differences were not detected between groups. In GFT a decrease of heart rate was recorded after eight hours from administration: it is not possible to differentiate between analgesic efficacy (disease resolution) and intrinsic vagotonic effect of fentanyl. A specific visceral pain scoring system does not exist for dogs and this could be an important limit of this study. Further studies are needed to verify the use of transdermal fentanyl solution (Recuvyra®) in dogs with pancreatitis.